1. Field of the Invention
Exemplary embodiments of the present invention relate to a wireless communication system; and, more particularly, to an apparatus and method for detecting a signal using correlation between orthogonal frequency division multiplexing (OFDM) symbols in a wireless communication system.
2. Description of Related Art
As an international standard for a wireless network, IEEE 802.11 has been introduced. Here, IEEE stands for the Institute of Electrical and Electronics Engineers. For example, IEEE 802.11a/g is a standard specification for a wireless local area network (LAN). IEEE 802.11a/g applies an orthogonal frequency division multiplexing (OFDM) modulation scheme as one of multi-carrier schemes. IEEE 802.11a/g supports a maximum data transmit rate of about 54 Mbps. However, a further higher data transmit rate has been required due to increasing demand for mess amount data.
In order to improve the data transmit rate, IEEE 802.11n has been developed as an extended standard of IEEE 802.11a/g. IEEE 802.11n applies an OFDM modulation scheme to a multiple-input multiple-output (MIMO) system.
The MIMO system includes a transmitter having a plurality of antennas and a receiver having a plurality of antennas. The MIMO system provides a high data transmit rate and improved bandwidth efficiency in a multi-path fading wireless channel environment using spatial-multiplexed multiple spatial streams. Further, IEEE 802.11n realizes high throughput (HT) by applying a modulation and coding scheme different from that of IEEE 802.11a/g.
IEEE 802.11n applies a new structured preamble having orthogonality for MIMO-OFDM time synchronization. Due to the new structured preamble, IEEE 802.11n cannot provide comparability with existing IEEE 802.11a/g WLNA equipment. In order to provide the comparability to the existing equipment, IEEE 802.11n draft standard provides three modes and defines different preambles for each mode.
Particularly, IEEE 802.11n draft standard introduced a Non-HT mode, a HT mixed mode, and a HT Greenfield mode. The Non-HT mode is identical to an existing preamble of a WLAN. That is, the Non-HT mode is a legacy mode and its preamble is a legacy preamble. The HT mixed mode is combination of the legacy preamble and a HT preamble. The HT Greenfield mode is for a high data transmit rate.
In the HT mixed mode, a packet includes a header formed of a legacy preamble and a HT preamble. Here, the legacy preamble is a preamble having a format introduced in IEEE 802.11a/g and the HT preamble is a new preamble introduced in IEEE 802.11n. Accordingly, such a HT mixed mode enables an IEEE 802.11n terminal to communicate with an IEEE 802.11a/g terminal.
In the HT mixed mode, an IEEE 802.11n transmitter uses a predetermined MCS (Modulation and Coding Scheme) method to inform a receiver of HT transmission. The receiver detects a HT preamble by comparing an I-phase component and a Q-phase component based on a received OFDM signal from the transmitter. However, the receiver may erroneously detect the HT preamble when the HT preamble is detected only based on the I-phase component and Q-phase component. Although a success rate of detecting a HT preamble may be improved by controlling a detection range of the I-phase and Q-phase components, performance thereof significantly decreases when a signal to noise ratio is low.
Therefore, there has been a demand for developing an apparatus and method for detecting a HT preamble according to a modulation scheme in order to overcome the above described problems.